Automobile tires are formed using rubber compositions made from natural rubber and synthetic diene rubbers. The degradation of such tires is accelerated by high ozone or oxygen levels or by ultraviolet rays, which may result in cracks in the tires. In order to suppress crack formation and propagation in the presence of ozone, for example, antioxidants such as N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD) or poly(2,2,4-trimethyl-1,2-)dihydroquinoline (TMDQ) are incorporated in rubber compositions.
The antioxidants in rubber vulcanizates migrate (bloom) to the rubber surface of for example tires, thereby protecting the rubber from ozone. Unfortunately, excessive blooming of the antioxidants in a short period of time causes white discoloration. Moreover, the antioxidants oxidized by ozone cause brown discoloration, and they excessively bloom as above, thus intensifying the brown discoloration. Furthermore, if the wax, antioxidants, and other components deposited on the tire surface form an uneven bloom layer (surface-protecting layer), diffuse reflection of light occurs, making the brown discoloration caused by the degraded antioxidants more noticeable. It has thus been difficult to improve ozone resistance while preventing discoloration.
Patent Literature 1 describes that the incorporation of a polyoxyethylene ether nonionic surfactant prevents deterioration of the appearance of tires. However, no technique has been developed that satisfies all the properties: fuel economy, durability (discoloration resistance and ozone resistance), and high tensile strength.